Bird of The Week: Blue Grosbeak
“Big-billed Bunting” Grosbeak. Photo by Mike Parr.
Scientific Name: Passerina caerulea
Population: 20 million
Habitat: Breeds in open, shrubby fields, hedgerows, and along forest edges; winters along dry tropical forest edges and in weedy fields.
About the Blue Grosbeak
Although the male Blue Grosbeak is colorful, this chunky, finch-like bird of brushy habitats is often first detected by voice. Once seen, a male Blue Grosbeak is distinctive, with deep-blue plumage set off by two rust-colored wingbars.
Like the Black-throated Blue Warbler, the genders of adult Blue Grosbeaks can be easily discerned thanks to very different plumages (a phenomenon scientists call sexual dimorphism). The female is a subdued mixture of tawny and rusty brown, sometimes with a few blue feathers mixed in. Both sexes have large, conical bills and blackish wings and tails. Unlike the similarly hued but smaller Indigo Bunting, this grosbeak habitually flicks and spreads its fairly long tail as it sidles through the undergrowth or perches on wires and fences.
Although this bird is called a “grosbeak” (literally, large bill), it isn’t necessarily related to other birds with the same name.
The most recent mitochondrial DNA research places the Blue Grosbeak in the Passerina genus, meaning that it’s most closely related to Lazuli, Indigo, Painted, and Varied Buntings, rather than to similarly named birds like the Evening Grosbeak, which is actually a member of the finch family.
Song and Sounds
In his field guide, David Allen Sibley aptly describes the Blue Grosbeak’s song as “a rich, husky warble with distinctive unbroken tempo and mumbled quality….” Although easy to hear, this rambling song can go unnoticed, especially when heard from some distance.
Only males are known to sing, but a distinctive call note is uttered by both sexes — a loud, metallic “chink” that is often the first clue that a Blue Grosbeak is in the area.
Breeding and Feeding
The Bluest Breeder
Male Blue Grosbeaks declare territory and attract a mate through song. This species is monogamous during its breeding season, and a male will guard his mate by following her around as she feeds. As with other blue-colored birds such as the Mountain Bluebird, the rich coloring of the male Blue Grosbeak is a result of refracted light, and much of it is in the ultraviolet range — invisible to the human eye. It is thought that perhaps a male’s color indicates his breeding quality, and that this probably influences a female grosbeak’s selection of a mate.
The female Blue Grosbeak builds her cup-shaped nest within thick vegetation, usually three to 10 feet above the ground. She uses twigs, rootlets, and other vegetation for the outer layer. Like the Great Crested Flycatcher, when constructing the nest, she will often incorporate bits of snake skin, the scent of which may repel potential predators. The interior of the nest is lined with finer materials such as animal hair. The female then lays a clutch of three to five eggs. The male brings her food while she incubates, usually for 11 to 12 days. Both parents feed the chicks after they hatch. Once her first brood leaves the nest, though, the female will build a second nest and lay a second clutch, while her mate continues to care for the first-brood fledglings.
Feeding with Friends
The Blue Grosbeak’s large bill allows it to easily take large insect prey such as mantids, beetles, cicadas, and grasshoppers. This bird adds grass and weed seeds to its diet during migration and in winter, and also feeds on waste grain such as corn, rice, and oats in agricultural fields. It forages by hopping around on or near the ground, or hovering to glean prey from vegetation. Outside its nesting season, the Blue Grosbeak is social, often seen foraging in small flocks.
Region and Range
Originally a nester in the southern and central United States, Mexico, and western Central America, the Blue Grosbeak has been expanding its breeding range northward. The species now nests as far north as northern New Jersey and Illinois, and even south-central North Dakota, for reasons not entirely understood.
This species is a short-distance migrant, moving only as far south as Mexico, Central America, and the Caribbean to spend the winter. In some parts of central Mexico and Central America, the Blue Grosbeak is a permanent resident and does not migrate.
Conservation of the Blue Grosbeak
Although widely distributed, the Blue Grosbeak is usually found in rather low numbers. Much more remains to be discovered about its nesting habits and wintering grounds. Its nests are often parasitized by Brown-headed Cowbirds, but adult grosbeaks have been known to recognize and eject the intruders’ eggs. During migration, Blue Grosbeaks can fall victim to collisions with windows, wind turbines, and communications towers, or be preyed upon by outdoor cats.
Policies enacted by the U.S. Congress and federal agencies, such as the U.S. Fish and Wildlife Service, have a huge impact on migratory birds. You can help shape these rules for the better by telling lawmakers to prioritize birds, bird habitat, and bird-friendly measures. To get started, visit ABC’s Action Center. Living a bird-friendly life can have an immediate impact on migratory birds in the United States. Doing so can be as easy as adding native plants to your garden, avoiding pesticides, and keeping cats indoors. To learn more, visit our Bird-Friendly Life page.
Source: American Bird Conservancy (abcbirds.org)